Distance and speed control devices, or ACC (adaptive cruise control) systems, may be used in motor vehicles. In these systems, objects, such as preceding vehicles, which are in the traffic lane being used by one's own vehicle are detected by a sensor device. Conventionally, the sensor device includes a radar system with which the distance and the relative speed of the preceding vehicle can be measured. With the help of a direction-sensitive radar system or through the aid of additional parameters, e.g., the steering wheel angle of one's own vehicle, the detected objects may be checked for their plausibility so that, for example, vehicles in one's own lane can be distinguished from traffic signs or markings on the edge of the roadway or from vehicles in other lanes. If a preceding vehicle in one's own lane is in the locating range of the radar, the traveling speed may be regulated in such a way by intervention in the drive system and braking system of the vehicle, that a speed-dependent safety distance to the preceding vehicle is maintained. If, however, no vehicle is in the locating range in one's own lane, then control may be carried out to a speed, desired by the driver and input with the aid of a set command, which, in the following, is denoted as “set speed”.
German Patent No. 42 00 694, describes an ACC system in which the control is temporarily canceled when the driver intervenes actively in the driving events, for example, by activating the turn signal indicator. Therefore, the control is inactivated in particular when the driver starts to pass. After a certain time span has elapsed, if the passing maneuver is concluded, the control sets in again automatically; in the event of a permanent traffic lane change, a different target object located in the new traffic lane is may be monitored.
In German Patent Application No. 198 21 122, a system is described in which, when the driver (in regions with right-hand traffic) activates the left turn signal lever and thus indicates a desire to pass, the distance control is not inactivated, but rather the setpoint distance to the preceding vehicle is temporarily reduced to a specific minimum value. The result is that in preparation for the passing maneuver, the vehicle is automatically accelerated or less strongly decelerated than would be the case during the normal distance control. This makes it easier for the driver to slip into the traffic flowing in the passing lane, and the passing distance is shortened without the driver having to actively actuate the accelerator. On the other hand, the danger of a collision with the preceding vehicle is avoided, since a certain minimum distance to the preceding vehicle is always honored.
This system may relieve the driver when initiating the passing maneuver so that he/she can concentrate more on the rear traffic; however, the system may not react appropriately in all traffic situations. If, for example, a relatively slow vehicle is driving in the passing lane, following the acceleration phase, a relatively strong deceleration of the vehicle is necessary if the lane change was carried out and the slow vehicle in the passing lane has gotten into the locating range of the radar. The acceleration, uncalled for in this situation, and the subsequent deceleration of the vehicle leads to increased fuel consumption and an adverse influence on comfort and possibly even on traffic safety.
German Patent Application No. 197 57 063, describes an ACC system in which the radar system also measures the relative speeds of vehicles in the passing lane and continually forms an average value from these relative speeds. When a desire by the driver to pass is detectable, acceleration is automatically carried out to an increased traveling speed as a function of this average value. However, inadequate reactions may occur in this system as well, since the speeds of the vehicles in the passing lane are only evaluated statistically.
In German Patent Application No. 196 37 245, an ACC system is described in which the plausibility evaluation of the radar signals is modified when the driver indicates the intention to change lanes by actuating the left or right turn signal lever. In this situation, the traffic lane taken into consideration for the distance control is temporarily expanded to the future new traffic lane, and both the vehicles in the present traffic lane and the vehicles in the future traffic lane are taken into account for the distance control along the lines of a minimum selection. In this way, a consistent distance control is made possible both for a lane change from the right to the left traffic lane, as well as for a change from the left to the right traffic lane; however, no increase in the driving speed takes place to prepare for the passing maneuver.